An organic EL device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials. Tang et al. used tris(8-hydroxyquinolinolato)aluminum for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excitons which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excitons formed within the light emitting layer can be enclosed. As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
As the light emitting material, chelate complexes such as tris(8-quinolinolato)aluminum, coumarine derivatives, tetraphenyl-butadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (for example, Patent Reference 1, Patent Reference 2 and Patent Reference 3).
As the light emitting material, a benzanthracene derivative having an aromatic hydrocarbon ring at the 12-position is disclosed in Patent Reference 4. The benzanthracene derivative is used as the light emitting material emitting blue light. However, the benzanthracene derivative has drawbacks in that the obtained device does not have a sufficient life and does not exhibit excellent chromaticity.
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 8 (1996)-239655
[Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 7 (1995)-138561
[Patent Reference 3] Japanese Patent Application Laid-Open No. Heisei 3 (1991)-200889
[Patent Reference 4] Japanese Patent Application Laid-Open No. 2000-178548